CIRCULATION. 457 



Nature of Vagus Influence on Heart. The nature of the terminal 

 apparatus by which the vagus inhibits the heart is unknown. It is probable 

 that the same intracaidiac apparatus serves for both nerves, for Hufler finds 

 that when the heart escapes from the inhibition caused by continued stimula- 

 tion of one vagus, the prolonged diastole growing shorter again, the immediate 

 stimulation of the second vagus has no effect upon the heart, 1 Dogiel and 

 Grahe have recently observed that the lengthening of diastole which follows 

 stimulation of the peripheral stump of the vagus, the other vagus being intact, 

 is less marked than when both vagi are cut. 2 



The question whether the vagus acts on the heart muscle directly or through 

 the medium of some nervous mechanism has not yet been answered. The only 

 fact bearing immediately on this problem is the diminution in the irritability of 

 the ventricle during vagus excitation, and this does not exclude an action upon 

 a nervous mechanism. 3 



The earlier attempts to form a satisfactory theory for the inhibitory power 

 of the vagus met with little success. The statement of the Webers' that the vagus 

 inhibits the movements of the heart gave to nerves a new attribute, but is 

 hardly an explanation. The view of Budge 4 and Schiff, 5 that the vagus is the 

 motor nerve of the heart and that inhibition is the expression of its exhaustion, 

 is now of only historical interest. Nor has a better fate overtaken the theory 

 of Brown-Sequard, 6 who saw in the vagus the vaso-motor nerve of the heart, 

 the stimulation of which, by narrowing the coronary arteries, deprived the 

 heart of the blood that, according to Brown-Sequard, is the exciting cause of the 

 contraction. 



Of recent years, the explanation that has commanded most attention is the 

 one advanced by Stefani 7 and Gaskell, namely, that the vagus is the trophic nerve 

 of the heart, producing a dis-assimilation or katabolism in systole and an 

 assimilation or anabolism in diastole. Gaskell supports this theory by the 

 observation that the after-effect of vagus excitation is to strengthen the force 

 of the cardiac contraction and to increase the speed with which the excitation 

 wave passes over the heart, while the contrary effects are witnessed after the 

 excitation of the augmentor nerves. 8 



Various attempts have been made to prove a trophic action of the vagus on 

 the heart by cutting the nerve in animals kept alive until degenerative changes 



1 Hufler, 1889, p. 307 ; Hough, 1895, p. 198. Earlier experimenters obtained conflicting 

 results ; see Tarchanoff and Puelma, 1875, p. 757 ; Tarchanoff, 1876, p. 296 ; Eckhard, 1879, p. 

 181 ; Gamgee and Priestley, 1878, p. 39 ; Tscherepin, 1881 ; McWilliam, 1885, p. 217 ; Mills, 

 1885, p. 257 ; Laulanie, 1889, p. 377. 



2 Dogiel and Grahe, 1895, p. 393. 



3 Changes in the peripheral efficiency of the vagi are discussed by McWilliam, 1893, p. 475. 



4 Budge, 1846, p. 418. 5 Schiff, 1849, p. 442. 



6 Brown-Sequard, 1853, p. 154. 



7 Stefani, 1880 ; 1895, p. 176 ; Eichhorst, 1879, p. 18 ; Gaskell, 1886, p. 49 ; Fantino, 1888, 

 p. 243 ; Timofeew, 1889 ; Tigerstedt, 1893, p. 259. Gaskell gives a re'sume' of his work on the 

 heart in Archives de Physiologic, 1888, pp. 56-68. 



8 Gaskell, 1883, pp. 81, 94; also Gianuzzi, 1871; Schiff, 1878, p. 16; Brown-Se'quard, 1880, 

 p. 211 ; Laffont, 1887, p. 1095 ; Konow and Stenbeck, 1889, p. 414. 



